1. Technical Field
This invention relates to a rotational direction switching clutch unit used e.g. in office machines.
2. Background Art
In a paper feed mechanism of an office machine such as a copier, in order to switch the paper feed direction between forward and backward, it is necessary to selectively connect the paper feed mechanism to one of forward and reverse rotational driving sources, thereby selectively driving the paper feed mechanism in the forward or reverse rotational direction.
For this purpose, it is known to use a rotational direction switching clutch unit using a spring clutch (Patent document 1, FIG. 3).
The clutch unit disclosed in Patent document 1 includes an output gear having a boss portion, and an input gear having a boss portion rotatably fitted around the boss portion of the output gear. A spring presser is threaded onto the front end portion of the boss portion of the output gear. A coil spring as a spring clutch is tightly wrapped around the radially outer surface of the boss portion of the input gear. A control gear is fitted around the coil spring. In order to lock and unlock the spring clutch, the control gear is selectively turned in one and the other directions, thereby twisting the coil spring in one and the other directions and radially expanding and compressing the coil spring. The input gear is coupled to a driving source for forward rotation. The control gear is coupled to a reverse rotational driving source through a rotation delaying device and an electromagnetic clutch. A reverse input transmission gear which is branched from the rotation delaying device meshes with the output gear.
In this clutch unit, when the spring clutch is locked, driving force in the forward rotational direction is transmitted to the output gear through the spring clutch. In this state, when the electromagnetic clutch is turned on, the driving force in the reverse rotational direction is transmitted to the control gear, so that the spring clutch is unlocked and transmission of driving force in the forward rotational direction is shut off. Then, with a time delay due to the rotation delaying device, reverse rotation is transmitted to the output gear. The rotation delaying device is provided to compensate for the delay in clutching action when the spring clutch is compressed and expanded, thereby ensuring transmission and non-transmission of driving force.    Patent document: JP Patent Publication 2002-154727A (“Embodiments” and FIGS. 3 and 4)
This rotational direction switching clutch unit requires the control gear to selectively radially expand and compress the coil spring as the spring clutch, and also the transmission gear for reverse input. The clutch unit further needs the rotation delaying device to compensate for the delay in clutching action of the spring clutch. Thus, this clutch unit requires a large number of component parts and complicated in structure, and is thus costly.